(i) Related Invention
This invention is an improvement on U.S. Pat. No. 5,865,277, patented Feb. 2, 1999, by Marc Hunter, the entire contents of which are incorporated herein by reference.
(ii) Field of the Invention
This invention relates to a brake system and brake actuator system for trucks. In one embodiment, it is particularly concerned with pneumatic air braking systems which are used on large trucks which are used in the forestry trucking industry.
(iii) Description of the Prior Art
Drum brakes are known to have certain advantages over disc brakes. Those advantages include superior braking force in some situations, and, the continued application of braking force where temperature variations occur while the brake is on.
A problem, however, with prior art drum brake assemblies was that they were of complex construction and assembly, and they were generally comprised of a large number of components and parts. Such a large number of parts resulted in the brake assembly being expensive, and time-consuming to both assemble and to fix to a vehicle.
A further problem with drum-type parking brake assemblies was that the drum shoe friction linings did not become properly-bedded by wearing against the inner surface of the drum. Unless there was a near-perfect match between the diameters of the lining when the brake was applied and the drum, the drum shoe would not properly-contact the drum over its entire surface and thus, an inferior braking force would result.
Drum brakes which included a plurality of brake shoes which were expanded within a brake drum attached to a wheel, required an actuating system to expand the brake shoes. In one type of actuating mechanism, the shoes were expanded by a cam, which was mounted on a shaft which was supported by bearings carried by a backing plate and by a spaced support which was fixed to an un-sprung part of the vehicle. The cam shaft generally extended between the backing plate and the spaced support in a direction which was substantially-parallel to the axle or to the axle housing to which the backing plate was fixed.
In mechanisms of the above-described type, the spaced support was welded or bolted to the axle or to the housing itself. In either case, however, the cam shaft bearings in the backing plate and in the support had to be in exact alignment to prevent binding of the cam shaft therein when completely assembled. It was known that, after the bracket was welded or bolted into place, unless extreme care was taken, the bearing in the bracket did not exactly align with the bearing in the backing plate. This caused the shaft to bind in its bearings. When the parts were welded into place, for maximum strength, the difficulties of securing proper bearing alignment were increased. During the manufacture of the backing plate and the support, they were stamped or otherwise formed, and usually had the necessary holes, etc., bored into them before they were welded to the axle or to the housing. While the customary jigs or other devices could be used to hold them in position during welding, it was extremely-difficult to hold them in the exact desired position so that when welded into place they would be properly-aligned for the attachment of other parts. It was also necessary accurately to machine the parts. Such proper alignment was particularly-necessary in the case of the spaced-bearings for the cam shaft.
Conventional brake mechanisms for automobile and truck wheels usually included a cylindrical brake drum which was mounted for rotation with each wheel. Pairs of semi-cylindrical brake shoes were mounted on the opposite sides of an axle housing for pivotal movement inwardly and outwardly between expanded and contracted positions. Brake linings were positioned between the brake shoes and the brake drums and were compressed therebetween incident to brake shoe expansion. Cams were positioned between free ends of the brake shoes for urging them into expanded positions and releasing them for spring contraction. The cams were controlled by linkages which were connected to a foot pedal or hand lever of the vehicle. When the brake lining wore out there was brake failure and the cam was normally ineffective to apply the brakes in such a manner as to stop the vehicle. This could also result from excessive heating and expansion of the brake drums so that proper shoe engagement could not be attained.
One current drum brake system has shoes that make contact with the drum. The wheel cylinder activates the shoes at the top, while there is separate linkage that is operated by a cable which throws out the shoes to come into contact with the drum. It also needs to be adjusted, but often it becomes rusty and therefore is not possible to adjust.
In most drum brakes, whether actuated manually, hydraulically or pneumatically, the arcuate brake shoes were interconnected by retraction springs. When the brakes were not applied, the brake shoes were held away from the rotating drum by the retraction springs. When the brakes were applied, e.g., in a hydraulic or pneumatic system, pressurization of the hydraulic or pneumatic cylinder forced the piston links outwardly from the cylinder against the brake shoes and caused the brake shoes to engage the rotating brake drum.
However, it was found in practice that the retraction springs occasionally became inoperative. The need, therefore, arose to provide brakes whose retraction was not provided by spring means, but which would be positively-actuated.
Heretofore, it was also a conventional practice in brake constructions to utilize relatively-inflexible brake shoes which had generally been reinforced against flexing by stiffening webs. Such brake shoes were pressed against a rotating drum by applying a force to an end of one shoe by means, e.g., of a pneumatic cylinder, or of a hydraulic cylinder, and provided an anchor at an opposite end of the shoe for anchoring the shoe against the circumferential-movement with the drum. It was also a conventional practice in such constructions to link together a pair of torque shoes at adjacent ends, whereby a single cylinder could be utilized for applying an actuating force at a free end or at an opposite end of a first shoe in the pair and whereby a single anchor could be located at the adjacent free end of a second shoe in the pair to receive friction forces which were developed along the surfaces of both of the shoes of the pair. In the latter arrangement, the frictional force which developed along the surface of the first shoe was transmitted to an end of the second shoe as an actuating force.
In conventional air brake systems, pressurized air was supplied by way of a service brake (control) line and an emergency brake (supply) line. The control line is connected through a relay valve to operate service brakes which are associated with each wheel pneumatically. In order to assure that the service system had adequate volume to provide for repeated service brake applications, the braking system further included a service reservoir or tank which was connected through the relay valve so that pressure may be supplied to the service brakes from a relatively large storage volume. The reservoir was pressurized through the supply (emergency) pressurization system which also provided pressure to the emergency or parking brakes of the vehicle. The emergency or parking brakes were generally spring-operated with the force of the springs being offset to release the brakes by the use of pressure within the emergency supply system.
In the pneumatic system of prior art air brake systems, the emergency brake was either an air pot with an auxiliary air tank separate from air lines, or a separate system which was reliant on the S-cam system. In such pneumatic system, when the air lines lost air pressure, a valve sensed the loss of air pressure and let all the air from the auxiliary tank. The air would eventually seep out and leave no pressure in the air pots. Thus, it was necessary to use blocks of wood as a back-up.
The S-cam system worked differently. It was not reliant on an auxiliary air tank, since this system included a spring in the air pot. When brake pressure was applied it compressed the spring, thus alleviating pressure from the shoes. A problem with such brakes is that a failure of the spring operating system could result in brakes loosing their braking power, resulting in dangerous operation of the vehicle.
Failure of conventional brakes was frequently-experienced on trucks, truck-trailers, or semi-trucks especially when carrying heavy loads. This usually occurred when the truck was descending a steep grade requiring repeated application of the brakes necessary to maintain a controllable speed. Runaway trucks, due to brake failure, have caused the loss of many lives of truck drivers and motorists in the paths of the trucks, and caused the loss of valuable cargo.
As noted above, the brakes were operated by brake actuators. Brake actuators of numerous configurations are thus known. Mechanical drum brake actuators generally operated to transmit force which was generally applied by a cable mechanism to two semi-circular brake shoes, thereby applying force to a brake drum and achieving the braking function. A conventional brake actuator typically forced the shoes against the drum through a piston or strut that was connected to an operator. Such brake actuators generally included an undesirable number of component parts which complicated assembly and typically permitted undesirable vertical or transverse movement of the mating shoe ends.
The prior art has provided mechanical brake actuators for shoe-drum brakes. In one known form of such an actuator, a force input lever and strut member were pivotally-interconnected and were adapted for engagement respectively with outer end portions of the shoes of a drum brake. The actuator was expandable by application of force to the lever in order to apply the shoes to the brake drum. In this known actuator, portions of the lever and strut member were supported for sliding-movement parallel to the brake backplate on surfaces fixed relative to the backplate, in order to react forces generated in these components in one direction perpendicular to the backplate. Such sliding-movement can, however, be undesirable in that it tended to adversely-affect the brake efficiency.
It was also known to provide a one-piece mechanism in the form of a strut which engaged the webs of a pair of brake shoes. The strut was pivotable in order to expand the shoes and was supported on a surface of a fixed abutment member by way of a roller engaging a surface of the member adjacent to the brake backplate.
As noted above, trucks and trailers were generally provided with a diaphragm chamber into which air was forced for operating a lever for applying the brakes. If, for any reason, there should be a failure of the compressor to keep the proper amount of pressure in the pressure storage tank, or should an air-leak develop and thus bring about an emergency, or if the driver was descending down a steep hill and he suddenly found out there was not enough air pressure to apply the brakes, the results of this can be disastrous to the driver of the truck, other drivers, or to the contents of the truck.
The problem was said to be solved by the prior art by providing additional means which were a combination of both pneumatically-operated means and spring means which are adapted to cooperate with the brake mechanism of the truck, tractor or trailer for insuring that the above-recited accidents cannot happen. The conventional braking mechanism may be used wherein compressed air was allowed to flow into diaphragm chambers for applying brakes. The brake operating means may also include a suitable auxiliary mechanism with a compression spring which was biased to apply the brakes, but, by admitting compressed air to this auxiliary mechanism, this tendency of the spring was overcome and it was impossible for this spring to apply the brakes. However, if there should be a failure of air pressure, or a decreasing in the air pressure, the auxiliary mechanism would tend slowly to apply the brake. In the case of an abrupt failure of air pressure, whereby the operator would be powerless to apply the brakes, the auxiliary mechanism would be automatically released and its spring, which was ordinarily held in the inoperative position by the air pressure, would then become active and would automatically apply the brakes.
In recent years, much effort was spent on trying to develop a satisfactory mounting structure for the fluid motor, the cam shaft, and the associated interconnecting linkage of fluid-powered, cam-actuated brake mechanisms of heavy duty vehicles.
The problems to be solved in such mounting structures were numerous. One of the major problems in such mountings was the location of the fluid motor, which had to be in such a position that it could not be damaged by obstacles in the path of the vehicle. A second problem was in the mounting of the fluid motor, which had to be in such a manner that the cam shaft of the actuating mechanism was not subject to deflection when the brakes were energized. A third problem was in the mounting of the fluid motor and associated linkage, in which the cam shaft bearings had to be accurately-axially-aligned and the cam shaft axis had to be properly located relative to the brake shoes. A fourth problem was that the fluid motor of such actuating mechanisms had to be so mounted that there was no interference with the spring suspension or with the axle stabilization linkages.
Due to the many various forms of axles and stabilization mechanisms therefor, it has been necessary in the past to provide an entirely-different mounting structure for each of the various forms of axles and associated stabilization mechanisms rather than providing mounting structures which are of general applicability.
An accepted prior art commercial design in the air brake field had been to mount the actuating diaphragm or cylinder on the axle, with its axis normal to the axis of rotation of the brake cam shaft which extended parallel to the axis of rotation of the wheel to be braked. It was necessary to mount the actuator on the axle well towards the longitudinal center line of the vehicle in order to avoid interference with springs, radius rods, torque rods and other vehicle parts. Hence, the cam shaft was relatively-long and was supported at opposite ends in bearings in the bracket by which the actuator was mounted on the axle and in the brake backing plate respectively. This arrangement required special actuator mounting brackets which had to be accurately-located to align the cam shaft bearings. The undesirably long cam shaft was also difficult to align and then to maintain in alignment. It also had a tendency to bend during assembly and during high braking torque conditions while in operation.
Many patents have been proposed to solve the problems recited above.
U.S. Pat. No. 2,331,652, patented Oct. 12, 1943, by Lawrence R. Buckendale and assigned to The Timken-Detroit Axle Company, provided a brake mechanism, including clamping means for adjustably-clamping the bearing member carried by the support and thus permitting rocking of the bearing through a sufficient range to compensate for any misalignment during assembly. After assembly, the bearing, which had been properly located in the support to eliminate any binding of the cam shaft, was clamped against further movement, and thereafter under operating conditions both cam shaft bearings were thus held in a fixed position. This patent thus disclosed a brake mechanism in which fluid actuated motors and associated linkages were located in such a position relative to the axle housing that they were to a large extent protected from damage by road obstacles in the path of the vehicles.
U.S. Pat. No. 2,409,908, patented Oct. 22, 1946, by Isaac W. Simpkins, provided an improvement in a vehicle which had a pair of wheels which were equipped with conventional brakes as well as a brake lever. A diaphragm housing and piston were connected to the lever. A source of fluid under pressure was provided for admission to the diaphragm housing for moving the lever to apply the brakes. A second lever was connected to the first lever and had a cable extending therefrom. There was a compression spring secured to the cable which normally tended to move the brake lever to apply the brakes. There was also a connection between the spring and the source of compressed fluid for normally holding the spring against actuation of the second lever, as long as a predetermined pressure was present in the source of compressed fluid.
U.S. Pat. No. 2,516,160, patented Jul. 25, 1950, to Ralph K. Super and assigned to Timken-Detroit Axle Company, provided an improvement in an axle assembly wherein a wheel brake mechanism had a rotatable operating shaft which was mounted on a non-rotatable part of the axle. Also included was a fluid motor, an external flange on the non-rotatable axle part, and a motion transmitting mechanism interconnecting the motor and shaft so that actuation of the motor rotated the shaft to control the brake mechanism. It also included means for mounting the motor on the non-rotatable axle part with its axis substantially-parallel to the axis of the axle. Such means also included a common mounting bracket for the brake mechanism and motor attached to the flange and had an angularly-related motor support portion extending along the non-rotatable axle part away from the brake mechanism.
U.S. Pat. No. 4,702,352, dated Oct. 27, 1987, to Brian Ingram et al and assigned to Lucas Industries Public Limited Co., provided an automatic adjuster including a strut having two parts between which there was a non-reversible screw-threaded connection which permitted the effective length of the strut to be increased by relative rotation between the parts under the influence of an adjuster device. The adjuster device incorporated clutch means for controlling the relative rotation in response to the occurrence of excessive clearance between braking surfaces. One of the adjuster parts was coupled by unidirectional means to a relatively-fixed part of the adjuster to resist rotation of one adjuster part in a de-adjusting direction, but to permit rotation thereof in the adjusting position. In one convenient arrangement, the uni-directional means comprised two parts which were independently-movable axially, but which were keyed against relative rotation. One of the parts was non-rotatably-engaged with one adjuster part and the other of the parts was releasably-uni-directionally-coupled to the relatively-fixed part. The unidirectional means preferably included a pawl which was engagable with a ratchet on the relatively-fixed part. Conveniently, the ratchet could be of annular form and the unidirectional means had angularly-spaced arms, each carrying a pawl for arrangement with the ratchet.
U.S. Pat. No. 2,755,890, patented Jul. 24, 1956, by Walther F. Scheel and assigned to Rockwell Spring and Axle Company was directed to improvements in vehicle brake actuating mechanisms and was directed to novel mounting structures by which the cam shaft, its operating linkage, and an air or other fluid pressure powered motor could be mounted at varying distances from the wheel within the longitudinally-projected profile of the axle housing and without interference with the spring or other undergear of the vehicle. Special brackets were mounted in a novel manner upon an axle-mounted brake support that carried the brake shoes and associated parts. The brackets supported the fluid pressure motor, the brake cam shaft and the actuating connections therebetween. Thus, the patent provided, in combination, an axle housing, a brake mounting spider fixed to the axle housing adjacent to one end thereof, and brake shoe pivots on the spider at one side of the housing. A first brake actuating cam shaft bearing was mounted on the spider at the side thereof opposite to the brake shoe pivots. A longitudinally-apertured cam shaft support tube, and means for removably-mounting the tube upon the spider in coaxial-alignment with the bearing was provided and included interfitting pilot portions on the spider and one end of the tube. A second cam shaft bearing was provided within the end of the tube opposite to the spider. A motor mounting bracket, and means for removably-mounting the bracket on the other end of the tube in any of a plurality of positions which were angularly-displaced about the axis of the tube was provided for optimum protective location of the motor on the axle housing. A cam shaft was rotatably-mounted in the bearings and projected at its ends from the spider and from the tube. A motor was mounted on the bracket and was operatively-connected to the cam shaft.
Another patent was U.S. Pat. No. 2,949,171, patented Aug. 16, 1960, by Stanley P. Kissinger, provided an emergency brake controlling apparatus whereby, during normal operation, the brake shoes were expanded by rotation of a cam in the usual manner. The patented invention provided the combination with a support, of a pair of elongated controlled elements, and means pivotally-mounting the elements in the support for movement towards and away from each other. An apparatus was provided for controlling the movement of the elements and included receptacles which were connected to the elements and had opposed recesses. One of the recesses was substantially-semi-cylindrical and the other recess was fractionally-spherical. The semi-cylindrical recess was substantially-concentric to an axis which was parallel to the pivot axis of one of the elements. A telescopically-adjustable control member including a first end portion having a substantially-semi-cylindrical end key was complementarily-movably-fitted in the semi-cylindrical recess for pivotal movement around the axis of the semi-cylindrical recess, but was locked against rotation relative to its receptacle. A second end portion was expansible and contractible relative to the first end portion and had a fractionally-spherical, ball-shaped end which was complementarily-universally-fitted in the fractionally-spherical recess. Means were connected to the control member for effecting expansion and contraction thereof.
U.S. Pat. No. 4,887,698, patented Dec. 19, 1989, to Timothy J. Hunt et al and assigned to Lucas Industries Public Limited Company provided a mechanical brake actuator for a shoe drum brake. The mechanical brake actuator comprised an assembly which included a pair of pivotally-interconnected parts for co-action respectively with the brake shoes. One part was connectable to force-applying means and the other part extended, in use, between its associated shoe and the one part to form a strut, the parts were pivotally-interconnected by a pivot member which carried at least one roller arranged to engage, in use, a surface fixed relative to a backplate carrying the shoes. In one convenient arrangement, the fixed surface which was engaged by the roller was spaced inwardly from the backplate. Conveniently, it was on an abutment member on the backplate and was engageable by the adjacent shoe ends. Typically, in such an arrangement, the fixed surface was at the side of the shoe webs remote from the backplate. A pair of rollers could then be carried by the pivot member and arranged at either side of the actuator assembly. The rollers respectively-engaged surfaces of the abutment member at either side of the slot therein. Typically, the pivotal axis between the two actuator parts lay between the locations of engagement, in use, between these parts and the respective shoes.
U.S. Pat. No. 5,246,093, patented Sep. 21, 1993, to Nui Wang and assigned to Brake & Clutch Industries Australia Pty Ltd., provided a drum brake assembly which included a drum which was rotatable on an axis and had a radially-inner cylindrical surface, which formed a braking surface. A support and a brake member or a shoe was mounted on the support and was movable relative thereto. The brake shoe was of substantially-circular form and had a radially-outer face and at least one friction lining mounted thereto on the outer face and extended around the circular form. Actuating means, when actuated, caused the brake shoe to diametrically-expand such that the lining of the shoe contacted the inner surface of the drum and thereby provided a braking action to the drum. The shoe was of substantially-constant cross-sectional form along at least a major portion of its length. The cross-sectional form and the material from which the shoe body was made of was such that the shoe provided significant support for the lining along the entire length of the lining. The resilience of the shoe body was such that when the actuating means was released, the shoe diametrically-contracted to move the lining out of contact with the inner surface of the drum.
Still another patent was U.S. Pat. No. 5,531,298, dated Jul. 21, 1996, by Frank W. Brooks, Sr. et al and assigned to General Motors Corporation, provided a Brake Actuator. The patented brake actuator included an anchor which served the purposes of providing a housing and mounting features. Two pistons were slidably-carried by the anchor. A lever which engaged one of the pistons, and a strut, were pivotally-interconnected with the lever and engaged the other piston. Application of input force to the lever was transmitted therethrough and through the strut to the two pistons which were forced to move linearly in opposing directions to provide movement to the brake shoe and effect braking forces. The patented brake actuator included an anchor which had a mounting flange with an opening and had a bore which was oriented substantially-perpendicular to the opening. A first piston which had a first slot with a first socket was slidably-carried in the bore and engaged one brake shoe end. A second piston which had a second slot with a second socket was carried in the bore and engaged the other brake shoe end. A lever which had a third socket, extended through the opening of the anchor, engaged the first piston in the first socket and had a stop. A reversible strut which had a first cylindrical segment engaged the second piston in the second socket and had a second cylindrical segment which engaged the lever in the third socket, the first and second cylindrical segments were connected by a neck which was engageable by the stop of the lever.